I just posted a theory on this regarding another grimoire question in the thread. When winning inferno doubles matches, it appears the game client is doing the rank 1/2/3 calculations for 25/50/100 wins. However, unmodified doubles usually does not do this. The inferno modifier may be triggering a hard coded appeal to the wrong grimoire interface in the game mode and may be triggering back end grimoire score increases. Another possibility in your situation: the various kill ranks supposedly do not always trigger the score increases associated with them. If yours did not all trigger where others' did, this could explain the score differential between you.